Pulp screening apparatus



July 20, A c, D M N 2,684,154

PULP SCREENING APPARATUS Filed July 18, 1950 3 Sheets-Sheet 1 |IH H 62 M 56 Ml INVENTOR.

Arthur 0. Damon ATTORNEY July 20, 1954 A. c. DAMAN 2,684,154

PULP SCREENING APPARATUS Filed July 18, 1950 s Sheets-Sheet FIG. -2

INVENTOR. Arthur 0. Damon BY 24%.4'2976 ATTORNEY July 20, 1954 c, DAMAN 2,684,154

PULP SCREENING APPARATUS Filed July 18, 1950 3 Sheets-Sheet 3 INVENTOR.

Arthur 0. Damon ATTORNEY Patented July 20, 1954 PULP SCREENING APPARATUS Arthur C. Daman, Denver, 0010., assignor to Mining Process and Patent Company, Denver, 0010., a corporation of Delaware Application July 18, 1950, Serial No. 174,471

15 Claims.

My invention refers to pulp screening apparatus which may be employed to separate a pulp consisting of various sizes of solid particles suspended in a liquid into at least two different size groups.

In various operations and particularly in the ore dressing field, it is necessary to separate an ore pulp into a first fraction containing particles exceeding a certain predetermined size and a second fraction containing all of the remaining particles. More specifically such an operation is frequently necessary before subjecting the ore to froth flotation which is in most instances adversely affected by the presence of extremely fine solid particles or slimes.

Various devices have been proposed for accomplishing this separation and have met with varying degrees of success in practice. Certain of these prior art devices have employed screens to affect the separation, but these have not been generally accepted despite their low cost and mechanical simplicity because they exhibit a marked tendency in operation to clogging or blinding of the screen. Difficulty has also been encountered in these devices with the elimination of unfilterable solids such as agglomerated particles having a density less than the density of the slurry. Regulation of pulp flow rates has also been troublesome due to the tendency of the pulp to clog or block valves or pipes heretofore necessary in the apparatus.

It is an object of my invention to provide a simple, durable and inexpensive apparatus for continuously screening pulp which incorporates means for substantially preventing clogging or blinding of the screen, which prevents segregation of the pulp, which separates the pulp into two components by a combined hydraulic classifying and screening action, provides proper circulation, means for discharging unfilterable solids from the device, means for conditioning the pulp by the introduction of one or more fluids and simple means resistant to clogging for regulating the rate of pulp flow in accordance with the desires of the operator. Other objects reside in the various novel combinations of component parts and will be disclosed in the following detail description and in the appended drawings in which:

Fig. l is a partial vertical section through a first form of my device;

Fig. 2 is a partial vertical section through a modified form of my device;

Fig. 3 is a partial plan view of my apparatus;

Fig. 4 is a partial elevation of the form of screen oscillating mechanism; and

Fig. 5 is a partial perspective view of a portion of my apparatus illustrating the means for discharging filtered material.

Referring to the drawings, in Fig. 1 I have illustrated a tank generally designated [0 having upright cylindrical side walls H and a conical bottom l2, the apex of which is provided with an outlet i3. Beams hi extend across the open top of the tank It] and support a member I! which is in turn secured to a hollow upright bearing housing It by brackets l8. A shaft i9 is journalled in the housing [6 and extends downwardly into the tank it. A driving sheave 2| is secured to the upper end of the shaft. The shaft is is preferably hollow and open at its lower end for discharging fluid such as air or water into the tank I I. The upper end of the shaft i9 is sealed. Fluid is preferably introduced through an inlet 22 formed in the housing 16 and passes into the shaft it through openings 23 formed in the shaft i9 within the housing It. Impeller members 24 are secured to the shaft l9 near its lower end and are of such configuration as to drive the pulp in the desired direction upon rotation of the shaft I9.

As an example of a suitable configuration, each of the impeller members 24 may be of triangular cross section with the apex of the triangle pointing downwardly whereby regardless of the direction of shaft rotation, pulp around the shaft [9 will be driven downwardly. A collar 26 engages the lower portion of the housing I6 and is secured at its periphery to the upper inner portion of the wall of a cylindrical member 27 which extends downwardly from the collar 26 around the shaft i9. The lower end of the member 27 is open to permit the flow of pulp into and out of the member 2'1. An imperforate disc 28 is secured to the lower portion of the member 2? and extends outwardly therefrom, being secured at its periphery to a cylindrical screen 29 which extends upwardly to approximately the lip of the tank Ii]. A transverse support strap 3i is secured to the upper lip of the screen 29 and to the upper extremity of the member 27.

Within the tank l0 and below the screen 29 is a battle generally designated 32. The upper portion 33 of the baffi 32 is cylindrical and extends upwardly a short distance above the lower extremity of the screen 29. If desired supports 34 may extend from the cylindrical portion 33 to the tank I!) for supporting the bafiie 32 in position. The lower portion 36 of the baflie 32 is 3 shaped in the form of an inverted cone and defines a relatively large bottom opening 37 aligned with a shaft 19 and the outlet 13. The baiiie 32 is spaced from the tank iii to define pulp flow passageways. An opening 38 is formed in the bafiie 32 for the passage of a flexible conduit 3% which connects the interior of the screen 29 with an outlet ii formed in a wall of the tank It. The outlet M is pivotally connected to a pipe d2 which extends from the outlet M in a direction generally parallel to the walls ll of the tank i8 in such manner that .the pipe 42 may be swung about its pivot to determine the maximum level of pulp within the screen 29. An outlet M is also formed in the wall ll of the tank it somewhat above the level of the outlet 4! and is pivotally connected to a pipe 45, similar to the pipe 42. The outlet [3 may be provided with a valve 45 or may be pivotally connected with a pipe 41, one portion of which extends upwardly generally parallel to the tank wall ii and movable about i-ts pivot to fix the level of pulp within the tank l0,

An inlet pipe 48 communicates with tank It through the outlet !3 and may be used when desired for the introduction of conditioning fluid such as air or water. A feed launder :39 extends downwardly over the lip of the tank l and discharges into a downwardly extending inlet pipe the outlet of which is preferably disposed below the level of pulp in the tank it. Thus in operation the pulp to be screened flows into the tank it! through the launder 49 and the pipe 5!.

In operation, the tank is filled with pulp to a first level indicated at 52 which is determined by angular movement of the pipes 4 1 and 43 and/ or by regulation of the valve 46. It will be understood that if the pipe 41 is pivotally connected to the outlet 13, the valve 46 is unnecessary and may be eliminated. The pipe 42 is moved angularly to permit, discharge of pulp from within the, screen 29 at a level such as level 53 which is below the level 52. The difference between the levels 52 and 5,3 establishes a hydrostatic head across the screen 29 which servestof orce liquid 1 and solid particles, smaller than the openings in the screen 29 inwardly past the screen 29 and subsequently outwardly through the conduit 39 and the pipe 42.

Ordinarily the screen 29 would quickly become blinded or clogged by the deposition of solid particles upon the screen. To prevent this, the screen 29 is oscillated about its axis by an arm 54 pivotally connected to a stud 55 secured to the strap 31. The opposite end of the arm 5 is pivotally connected to a crank or eccentric 5? which is in turn driven by shaft 58. In addition, an electric vibrator 59 or the like is connected to a rigid strap 6| which is in turn secured to the member 2'! thereby transmitting the vibrations generated by the vibrator 59 to the screen 29. During operation, the shaft [9 is also rotated as by the sheave 2i and operates to force pulp from within the member 2? downwardly through the opening 31 in the baflie 32 towards the outlet E3. The heavier particles in the pulp will settle by gravity on the bottom i2 of the tank it and will be moved due to the inclination of the bottom towards the outlet 13. These particles are, how ever, continuously washed by the stream of pulp which passes upwardly between the outer surface of the bafiie 32 and the side and bottom walls of the tank If! to the lip of the baifle 32 where they again enter the interior of the baffle and are forced downwardly through the opening 3'5. This current formed by the impellers 24 on the shaft it aids in preventing blinding of the screen 29 by continuously washing the outer surface of the screen.

It will be understood that the pulp fed to the feed launder t9 and to the tank it will frequently contain lumps of undispersed solids and in some instances agglomerated particles formed in various manners as, for example, by the inclusion of conditioning agents with the pulp. These masses will be in part dispersed by the action of the impellers 24 on the shaft 19 and in part by the action of the conditioning fluids introduced through the inlet 48, the inlet 22 or through an alternative inlet 62 which extends through the housing It into communication with the interior of the cylindrical member 27. The agglomerated masses and other materials which tend to float in the tank are drawn off through the outlet 43 and discharged to waste or for subsequent process. Thus during operation, the screen 29 is continuously vibrated at a pre-selected frequency, oscillated in a limited are about its major axis and continuously sweptby currents generated in the pulp by rotation of the shaft l9.

Material discharged through the outlet {3 is substantially free of fine particles or slimes since it is continuously washed by the upwardly flowing currents generated by rotation of the shaft it. The effect of these currents and the washing of the pulp may be increased by attaching a suitable propeller 63 as shown in Fi 2 to the lower extremity of the shaft l9 immediately above the opening Also, if desired, a number of the impellers 24 on the shaft l5 may be inverted, thus creating a high order of turbulence within the cylindrical member 21 which aids in dispersing the solids in the liquid and in mixing the conditioning fluid with the pulp. It is also possible, if desired, to eliminate the vibrator 59 by substituting therefor an eccentrically mounted weight rid secured to the shaft [9. The effect of the eccentric weight it is to induce a vibration which is transmitted by the pulp to the member 21 and screen 29. Preferably the eccentric weight is adjustable to vary the amplitude of vibration. Adjustability may be attained by utilization of any of several well known mechanical expedients, as for example, by forming in the weight a plurality of shaft receiving openings each spaced from the center a different distance.

The choice between the forms of device illustrated in Figs. 1 and 2 will depend upon the characteristics of the material being treated. If the solids in the pulp have a high specific gravity and a high percentage of fines which must be removedfthe form shown in Fig. 2 is usually preferable since the velocity of the induced currents is greater. Also various changes may be made in the material specified without departure from the true spirit and scope of this invention. For example, the washer may be either of metal as illustrated in Fig. l, or of rube bar as indicated at 52' in Fig. 2. The conduit may be of rubber or of flexible metal tubing or the like as dictated by operating conditions. The downwardly extending feed pipe 5| may be eliminated as shown in Fig. 2 and other changes of similar nature which will be apparent to those skilled in the art may be incorporated.

I claim:

1. Apparatus for screening pulp comprising a tank having an inverted conical bottom and an axial outlet therein, an inverted conical battle in the tank bottom defining therewith a pulp circulation channel along the tank bottom, said baffle having an axial opening formed therein above the tank outlet, a generally cylindrical screen in the opening above the baffle defining a screen chamber, said screen including an axially disposed downwardly projecting tubular member sealed its upperend and open at its lower end, an imperiorate disk projecting outwardly from the lower portion of the tubular member, a cylindrical foraminous member secured to the periphery of the disk and projecting upwardly therefrom, said tubular member, disk, foraminous member defining a screen chamber, a rotatable shaft projecting downwardly into the tubular member, impeller means carried by the shaft for circulating pulp through the circulation channel, a conditioning fluid inlet for introducing conditioning fluid into the tubular member, means for oscillating the tubular member about an upright axis, a flexible discharge conduit communicating with the screen chamber for maintaining a predetermined pulp level therein, and overflow means on the tank for maintaining pulp level in the tank above the level of pulp in the screen chamber.

2. Apparatus for screening pulp comprising a tank having an inverted conical bottom and an axial outlet therein, an inverted conical bafile in the tank spaced upwardly from the bottom and defining therewith a pulp circulation channel, said baffle having an axially disposed opening formed therein above said tank outlet, overflow means for maintaining a predetermined pulp level in the tank, a hollow rotatable shaft projecting downwardly into the tank on the axis thereof and open at its lower end, means for injecting conditioning fluid into the tank through said hollow shaft, impeller means carried by the shaft for forcing pulp downwardly towards the tank outlet and upwardly through the said pulp circulation channel, a generally cylindrical screen defining a screen chamber and including a centrally disposed tubular member telescoped over the shaft and spaced therefrom, the lower end of said tubular member being open for free communication with pulp in the tank, impeller means carried by the shaft within the tubular member, a disk projecting laterally from the lower portion of the tubular member, and a cylindrical foraminous member secured to the periphery of the disk and projecting upwardly therefrom to a level above the level of pulp in the tank, said foraminous member being disposed at least partially in the path of pulp circulating through said circulation channel; means for supporting said cylindrical screen for movement about an upright axis, an arm pivotally attached to said screen for movement about a horizontal axis, means for reciprocating said arm, means including an eccentric weight secured to the shaft for vibrating said screen and a conduit for discharging pulp from the screen chamber, said conduit extending from the lower portion of the screen chamber through the tank at a point between the tank outlet and the level of pulp therein and having an outlet movable between predetermined levels for limiting maximum level of pulp within the screen chamber.

3. Apparatus for screening pulp comprising a tank having upright sides, the bottom portion of which slope toward a central discharge outlet, a submerged generally-annular bafiie in the lower portion of the tank having an open top and sloping sides terminating at a narrow bottom opening above and in proximity to the discharge outlet and defining with the tank a circulation channel for pulp, a central shaft journalled for rotation in the tank, a cylindrical member supported in the tank with a closed bottom in the plane of but spaced from the top of said baffle and including a tubular open-bottomed column concentric with the shaft and laterally spaced therefrom, means for feeding fluid into the upper portion of the column, fiuid-impelling means on the shaft within the column enclosure for causing a downward flow into and through the submerged baffle, the sides of said cylindrical member being foraminous to permit passage of liquid from the tank into its interiorunder differential pressures outside and inside said member, an inlet for pulp in the tank, a discharge line for liquid entering the cylindrical member having means for controlling the liquid level in said member, a discharge line for the circulating pulp in the tank having means for controlling the pulp level in the tank so as to maintain a hydrostatic pressure in the tank in excess of the level in said oscillatory member, a discharge line for settled solids passing through said central outlet, and means for rotating said shaft.

4. Apparatus as defined in claim 3, including means for oscillating said cylindrical member about an upright axis.

5. Apparatus as defined in claim 3, including means for vibrating said cylindrical member.

6. Apparatus as defined in claim 3, including means for simultaneously vibrating the cylindrical member and oscillating it about an upright axis.

'7. Apparatus for screening pulp comprising a tank having upright sides, the bottom portion of which slope toward a central discharge outlet, an inverted frusto-conical baffle in the lower portion of the tank with its bottom above and in proximity to the discharge outlet and defining with the tank a circulation channel for pulp, a central shaft journalled for rotation in the tank, a cylindrical member supported for oscillatory movement in the tank with a closed bottom in the plane of but spaced from the top of said bafile and including a tubular open-bottomed column concentric with the shaft and laterally spaced therefrom, means for directing a conditioning fluid through said column and into the bafiie enclosure, the sides of said cylindrical member being foraminous to permit passage of liquid from the tank into its interior under differential pressures outside and inside said member, impeller means at the lower end of the shaft for circulating pulp through said circulation channel, an inlet for pulp in the tank, a discharge line for liquid entering the cylindrical member, including a flexible portion carried by said member and means for controlling the liquid level in said member, a discharge line for the circulating pulp in the tank having means for controlling the pulp level in the tank so as to maintain a hydrostatic pressure in the tank in excess of the level in said oscillatory member, a. discharge line for settled solids passing through the central outlet, means for rotating said shaft, and means for oscillating the cylindrical member.

8. Apparatus as defined in claim 3 including impeller means at the lower end of said shaft beyond said fluid impelling means arranged to force pulp downwardly through the narrow opening in the baflie and upwardly through the circulation channel.

:9. Apparatus as definedvinclaim 3, -in,which the upright sides of.lthe1cylindrical member are screen material, the lower portionotwhich is at least partially in the path-of the circulating pulp.

.10. Apparatus as. definedin claim 3, in: which the shaft is hollow, and .meansareprovidedsior introducing a conditioning fluid through the shaft calmember has its upper end movable to selective elevations below the liquid level in the tank to thereby vary the pressure differential inside and outside said member.

. 14. Apparatus as defined in claim 3, in which an eccentric weight is secured to a lower portion of the shaft in a .position. to impart a vibratory movement to the cylindrical member.

15. Apparatus as defined in claim 3, including a valve-controlled feed inlet having its point of discharge substantially below the liquid level of the tank.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 994,377 Cottrell June 6, 1911 1,040,804 Stanley Oct. 8, 1912 1,146,211 Stromberg July 13, 1915 1,309,219 Ruth July 8, 1919 1,710,208 Deitz 1 Apr. 23, 1929 2,016,647 McMartin Oct. 8, 1935 2,356,289 Wells Aug.'22, 1944 2,463,526 Dickson Mar. 8, 1949 2,500,965 Symons Mar. 21, 1950 

